000
FXUS63 KDTX 121905
AFDDTX
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
305 PM EDT Mon Mar 12 2018
.DISCUSSION...
Closed mid level circulation now anchored just north-northeast of
lake Superior, with the southern expanse of the associated height
falls now encompassing southeast MI. Trailing shear axis contained
within the back end of the exiting mid level trough axis will
maintain residence locally into the evening. This in combination
with a diurnally supported steep lapse rate environment and
sufficient moisture quality will maintain the potential for snow
shower development through early evening. A noted decrease in both
large scale ascent and thermodynamic support will then subsequently
diminish snow shower chances overnight. Some repositioning of the
pressure fields as the parent circulation digs southeast into the
lake Huron basin tonight may establish a smaller scale region of
enhanced low level convergence. Greater potential for a localized
response will focus over the Saginaw Bay/thumb region, where the
nocturnal timing could prove more efficient at generating some
accumulation.
Center of the closed low pivots from Lake Huron to western NY on
Tuesday. This movement will draw the western flank of the pronounced
mid level cold pool /-40C at 500 mb/ across the area during the day.
This process will capitalize on favorable diurnal timing to
establish an environment characterized by steep low-mid lapse rates
and convective depth nearing 7-8 kft. Passage of an attendant lake
aggregate surface trough will supplement this background ascent. A
corresponding increase in snow shower coverage expected from north
to south, possibly originating off from any ongoing activity that
fixates over the thumb tonight. Potential will exist for brief but
intense bursts of snow to emerge given the convective component,
leading to a quick accumulation and abrupt drop in visibility. As
noted today, a stronger mid March sun angle requires higher snowfall
rates to carry longer residence time to provide any meaningful
accumulation on pavement. Greater potential will lie across the
thumb should a more pronounced convergence band materialize,
particularly during the morning period. Accompanying weak cold air
advection will translate into slightly cooler readings relative to
Monday. Highs low-mid 30s.
Departure of the mid level trough axis and associated cold pool
timed coincident with the loss of diurnal support results in a quick
decrease in snow shower potential by late Tuesday evening. A
trailing pv feature pivoting through the mean trough will lift
through Tuesday night/early Wednesday, but seemingly lacks the
moisture depth or favorable diurnal timing to support a secondary
window for snow shower development. Otherwise, high amplitude mid
level troughing maintains residence through the midweek period.
Retention of a deep layer northwest flow ensures temperatures remain
on the cooler side of average Wednesday.
Northwest flow in conjunction with mid-level shortwaves aloft will
help produce the slight chance for lake effect snow showers across
the thumb, closer to the Lake Huron shoreline for both Thursday and
Friday. The bulk of SE MI, however, is expected to remain dry as a
dry airmass resides across the state through the weekend. Lake
effect snow chances across the thumb will taper off early Saturday
as flow turn from the northwest to the southwest, cutting off the
moisture source from Lake Huron. Otherwise, mid-level ridging and a
surface high pressure will help keep conditions dry for all of SE MI
through the weekend as temperatures push into the low to mid-40s on
Friday and lower 50s on Saturday. The next chance for precipitation
will move in Tuesday morning as low pressure tracks east from the
Central Plains into the Ohio Valley.
&&
.MARINE...
Northwest winds over the central Great Lake will increase tonight,
reaching into the 15 to 20 knot range over Lake Huron. Colder air
streaming in tomorrow will support a further increase, but more out
of the north direction, with winds peaking between 25 to 30 knots
over Lake Huron. Waves of 5 to 10 feet will build over the southern
Lake Huron basin by Tuesday evening. Small craft advisories have
been issued. Winds will then gradually weaken Tuesday night through
Wednesday as they slowly back toward the northwest as the gradient
relaxes.
&&
.PREV DISCUSSION...
Issued at 100 PM EDT Mon Mar 12 2018
AVIATION...
Areal coverage of IFR/MVFR snow showers will diminish early this
afternoon. None-the-less, lingering scattered snow showers will
likely persist late this afternoon into the early evening hours,
with VSBY dipping into IFR if caught underneath one of them. Warm
pavement temps likely preventing accumulation. Otherwise, light
northwest winds this afternoon, likely not increasing above 10 knots
until this evening. It appears enough low level moisture will linger
this evening/tonight to sustain MVFR ceilings. An isolated threat of
snow showers will persist overnight, but much better coverage and
development expected by Noon tomorrow.
For DTW...Warm pavement temps and surface temps above freezing
likely preventing accumulation this afternoon. Northwest winds not
picking up until this evening, could see gusts around 20 knots
overnight, but especially tomorrow with diurnal mixing kicking in.
/DTW THRESHOLD PROBABILITIES...
* Moderate in ceilings at or below 5000 ft.
* High for snow as precipitation type.
* Very low for northwest crosswind this evening through tomorrow.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
DISCUSSION...MR/AM
MARINE.......SF
AVIATION.....SF
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